In the Iranian capital, violent clashes between anti-government crowds and police have killed at least eight protesters. (photo, from bbc.co.uk)
The nephew of former presidential candidate Mir Hossein Mousavi is reportedly among the four protesters shot dead in Tehran, while the others died in the northern city of Tabriz.
Security forces reportedly opened fire in Tehran after losing control.
As the Shia Muslim festival of Ashura reached a climax, opposition parties had urged people to take to the streets.
According to opposition sources, people were chanting “Khamenei will be toppled”, a reference to Iran’s Supreme Leader.
Thousands of demonstrators are reported to have taken part in the protests, in defiance of official warnings.
According to initial reports, the security forces fired in the air in order to disperse the protesters. However several different reports said that at least one, and possibly as many as eight demonstrators, had been shot dead.
Quoted by the Iranian Fars news agency, police sources denied it, saying foreign media were exaggerating reports of unrest.
‘The month of blood’
Mr Mousavi was at the hospital where his nephew Seyed Mousavi was taken after being fatally shot in the heart at Enghelab Square.
Since the deaths in the immediate aftermath of the disputed elections and protests in June, fatalities had been rare.
Siavash Ardalan of BBC Persian TV says that the security forces clearly have to tread a fine line between not appearing weak but also not provoking opposition protesters.
Reports said police helicopters were seen flying over central Tehran as clouds of black smoke billowed into the sky.
The security forces on the ground clashed with protesters trying to reach central Enghelab Square, witnesses said. (map, from bbc.co.uk)
Opposition websites say the protesters were chanting “This is the month of blood”, and calling for the downfall of Iran’s Supreme Leader Ayatollah Ali Khamenei.
At the same time, crowds of pro-government demonstrators marched on Enghelab Street to voice support for Ayatollah Khamenei, witnesses said.
Protests were also reported in the cities of Isfahan and Najafabad.
Festival of Ashura
Tensions have risen in Iran in the past week, since influential dissident cleric Grand Ayatollah Hoseyn Ali Montazeri died aged 87.
Supporters of opposition leader Mir Hossein Mousavi have sought to use Shia religious festivals this weekend to show continued defiance of President Mahmoud Ahmadinejad’s government, even though they were denied the right to protest.
The opposition chose the highly significant festival of Ashura when millions of Iranians traditionally go onto the streets for ceremonies and parades, BBC Tehran correspondent Jon Leyne says.
The festival of Ashura mourns the 7th Century death of Imam Hussein, a grandson of the Prophet Muhammad.
Iranian television had live coverage of the Ashura ceremonies, including those in Tehran attended by President Ahmadinejad.